When you strip back the outer jacket of a standard AC power cord, the 3 wire plug color code inside dictates whether your device runs safely or becomes a severe shock hazard. Because color standards shifted globally over the last 50 years—and because old equipment frequently circulates in modern workshops—guessing based on a single region's rules is dangerous. Below is the exact mapping you need before you crimp a single terminal.

The Global 3 Wire Plug Color Code Reference

This table covers the standard single-phase, 3-wire (Line, Neutral, Ground) AC power cords used in residential and light commercial environments. Read across your region's column to identify the wire function.

Wire Function US / Canada (NEC/CEC) EU / IEC (Harmonized) UK (Post-2004) Old UK (Pre-1970s) AU / NZ (AS/NZS 3000) Terminal Symbol
Line / Hot / Phase
Carries the supply voltage.		 Black (or Red) Brown Brown Red Active (Brown or Red) L, X, or Brass Screw
Neutral / Grounded
Completes the circuit back to the source.		 White (or Grey) Blue Blue Black Neutral (Blue or Black) N, W, or Silver Screw
Earth / Protective Ground
Safety path for fault currents.		 Green, Green/Yellow, or Bare Copper Green/Yellow Green/Yellow Green Earth (Green/Yellow) E, G, ⏚, or Green Screw
Hospital Grade / Isolated
Specialty clean ground for sensitive electronics.		 Orange Jacket (IG wire inside is Green with Yellow stripe) N/A (Handled via separate PE) N/A N/A N/A Orange Triangle ⏚

Rows People Get Wrong (And Why It Matters)

The most dangerous trap in the 3 wire plug color code matrix is the Old UK vs. Modern IEC Neutral. In pre-1970s UK wiring, the Neutral wire was Black. In modern IEC/EU harmonized wiring, Black is sometimes used as a Line/Hot conductor in multi-phase setups, while Blue is Neutral. If you rewire a vintage British appliance using modern IEC color assumptions, you will connect the modern Black (Hot) wire to the appliance's chassis or neutral return, creating an immediate short or lethal shock hazard upon plug-in.

Similarly, in the US, DIYers frequently confuse the Equipment Grounding Conductor (Green/Bare)Neutral (White). While they are bonded together at the main service panel, they serve entirely different purposes downstream. The neutral carries normal return current; the ground only carries current during a fault. Swapping them at a 3-prong plug will cause GFCI breakers to trip instantly and can energize the metal chassis of the appliance during normal operation.

Safe Interpretation When Markings Are Faded

Old cords, UV exposure, and heat can bleach wire jackets until White looks Grey and Green looks Brown. Never guess. Use this 'Dead Cord' continuity test to definitively map the wires:

  1. De-energize: Ensure the cord is completely unplugged from any power source.
  2. Set your DMM: Switch your digital multimeter to the continuity/diode test mode (the symbol with the soundwave).
  3. Identify the Ground Pin: On a US NEMA 5-15P plug, this is the U-shaped or round pin at the bottom. Touch one probe to this metal pin.
  4. Probe the Stripped Wires: Touch the other probe to the exposed copper of each wire inside the jacket. The wire that yields a near-zero resistance reading (and triggers the DMM beep) is your Ground.
  5. Identify Hot vs. Neutral: Look at the two flat blades on the plug face. The Hot blade is 0.250 inches (1/4") wide. The Neutral blade is wider, at 0.312 inches (5/16"). Probe the respective blades against the remaining two wires to map them perfectly.

Regional Standards: Which Code Applies to You?

⚠️ Mains Voltage Warning: Working with line voltage (>50V AC) carries a risk of fatal shock or arc flash. Always verify circuits are dead with a tested meter before touching terminals. The OSHA 1910.304 Wiring Design and Protection standard mandates strict identification of grounded and grounding conductors. If you are hardwiring a cord into a junction box rather than a plug, local AHJ codes may require a licensed electrician.

Your physical location and the origin of the equipment dictate which standard you must follow. The IEC 60446 standard harmonized most of Europe, but legacy systems and distinct national plug types still cause confusion on the bench.

  • North America (US/Canada): Governed by the NEC (NFPA 70) and CEC. Uses the NEMA 5-15P (15A/125V) and 5-20P (20A/125V) plug styles. Strictly enforces Black=Hot, White=Neutral, Green/Bare=Ground.
  • Europe (EU): Governed by IEC standards and local adoptions (like VDE in Germany). Uses the CEE 7/7 (Schuko) or CEE 7/16 (Europlug). Colors are Brown, Blue, and Green/Yellow. Note that Schuko plugs are unpolarized, meaning Line and Neutral can be swapped depending on how the plug is inserted into the wall.
  • United Kingdom: Governed by BS 7671 (The IET Wiring Regulations). The IET Wiring Matters publication details the 2004 harmonization where the UK adopted EU colors (Brown/Blue/Green-Yellow) to align with the continent, abandoning the old Red/Black/Green scheme. Uses the BS 1363 plug, which uniquely contains an internal fuse.
  • Australia / New Zealand: Governed by AS/NZS 3000. Uses the AS/NZS 3112 plug (angled flat pins). Active is Brown, Neutral is Blue, Earth is Green/Yellow.

Physical Terminal Pinouts and Verification

Knowing the wire color is only half the job; you must terminate them to the correct physical pin inside the plug housing. Reversing Hot and Neutral on a polarized plug defeats the safety design of the appliance's internal switch, leaving the device energized even when turned 'off'.

US NEMA 5-15P / 5-20P Internal Wiring

When looking at the back of the plug (where the wires enter, facing the terminal screws):

  • Brass Screw (Hot): Connect the Black wire. This aligns with the narrower 1/4" flat blade on the plug face.
  • Silver Screw (Neutral): Connect the White wire. This aligns with the wider 5/16" flat blade.
  • Green Screw (Ground): Connect the Green/Bare wire. This aligns with the U-shaped pin.

UK BS 1363 Internal Wiring

The UK plug is highly engineered and requires precise wire routing to ensure the internal cord grip secures the outer jacket, not the individual copper strands.

  • Right Pin (Live/Hot): Connect the Brown wire. Must route through the fuse carrier.
  • Left Pin (Neutral): Connect the Blue wire.
  • Top Pin (Earth): Connect the Green/Yellow wire. This pin is longer and opens the internal safety shutters of a BS 1363 wall socket.

Verification Step: The 'Live' Polarity Test

After terminating the 3 wire plug color code connections and securing the cord grip, do not immediately plug in a load. Perform a live polarity check:

  1. Plug the newly wired cord into a known-good GFCI-protected receptacle.
  2. Set your DMM to AC Voltage (V~).
  3. Measure between the Hot slot and Ground slot: You should read nominal voltage (114V–126V in the US, 220V–240V in the EU/UK).
  4. Measure between the Neutral slot and Ground slot: You should read less than 2V (ideally 0V). If you read line voltage here, your Hot and Neutral are reversed.
  5. Press the 'TEST' button on the wall GFCI. The power must cut immediately. If it doesn't, your ground wire is improperly terminated or broken.